A Thrust-only Flight-control System as a Backup for Loss of Primary Flight Controls

If all control surfaces of an aircraft become inoperative, only the engine thrust can change the pitching and rolling moment balance to allow the aircraft to fly stably and land safely. In an effort to actualize such aircraft control while providing as normal an operating feel as possible, Mitsubishi Heavy Industries, Ltd. (MHI) developed a thrust-only flight-control system consisting of a flight-control law based entirely on increases/decreases in thrust, an automatic-landing control law, and a pilot interface. This system was tested and evaluated by a pilot in a domed simulator to ensure that the aircraft would be able to fly and land safely, even if all control surfaces become inoperative. The results of this test indicate the possibility of improving aircraft safety and increasing the survivability of crews and passengers in the event of loss of primary flight controls. |1. Introduction An aircraft-control system is designed to lower the probability of losing the aircraft through a multiplex redundant system. Failure of the control system, however, has occurred in past. In 1974, Turkish Airlines Flight 981 experienced a collapse of the aft cargo compartment floor associated with losing the cargo door. This damaged the control cables and made the aircraft uncontrollable. The aircraft crashed a minute later, claiming the lives of all on board. In 1989, United Airlines Flight 232 lost flight control because the hydraulic pressure for the control surfaces was lost due to the dispersion of engine parts while in flight. However, an off-duty pilot who had studied the throttle-only flight-control technique was on board, and with his help, the aircraft reached an airport. The aircraft lost balance just before touchdown, causing the aircraft to break apart and catch fire when a wing tip crashed into the runway, but more than half the people on board survived, and the worst-case scenario was avoided. Although these accidents indicate that a malfunction of the surface control system is fatal to flight control, there is a chance of being able to control the aircraft using only the engine throttles. However, such control is a special technique requiring exceptional piloting skills, and it takes considerable training time to learn. Even if the control technique is learned during training, if it is applied during an actual emergency situation, the workload on the pilot at that time will be at a maximum level. Hence, achieving a safe landing by controlling the aircraft as intended using only the engine throttles up until the moment of touchdown is extremely difficult.